Hmm. Now THIS is an interesting question! You know, I have a problem with it all together but I really think that has to do with upbringing. I mean, there is just NO way I would allow my son or daughter to have a girlfriend or boyfriend stay the night. Period. In fact, even at eighteen there is a lack of mental development and yet we consider them "adults". HA!!!!!!!!!! The fact is, children are not able to make that kind of decision (sexual activity) and understand its ramifications, so they should not be put into that kind of situation in the first place.
HB makes the point that they will find a way. This is quite true, however, I do not want to "appear" to be against casual sex. I AM against it. At least as far as children are concerned. I do not think allowing children to wear make up is wise. Or watch questionable movies. Or speak using foul language. Or drink alcohol (under adult supervision). The point is, as parents, we must establish boundaries and make it clear as to why they are not to be broached. It is not a "control" issue. It is a decency issue. It is how parents teach values. You remember those, don't you? Values? Some of us do.
HB is right. They are going to "do it". We did. My parents did. Their parents did. The point is, it is our responsibility to guide them towards understanding what it means to have self-respect. How to conduct oneself in society. My parents would NEVER have allowed me to bring a girlfriend over for the night. Never. Of course, I did hide one in my bedroom closet once.....HA!!!!!!!!!!!!!!!!!!!!!!!!!!!! True story but not for this post!!! HAHAHAHAA!!!
It is a matter of leading them in the right directions and showing them what is expected of decent society. Children actually DO look to parents for that kind of thing...believe it or not! It is important that we establish the tent poles of decency and build that for them.